Since the particles are accelerated by the voltage many times, the final energy of the particles is not dependent on the accelerating voltage but on the strength of the magnetic field and the diameter of the accelerating chamber, the dees. Cyclotrons can only accelerate particles to speeds much slower than the speed of light, nonrelativistic speeds. For nonrelativistic particles, the centripetal force required to keep them in their curved path is
where is the particle's mass, its velocity, and is the radius of the path. This force is provided by the Lorentz force of the magnetic field
where is the particle's charge. The particles reach their maximum energy at the periphery of the dees, where the radius of their path is the radius of the dees. Equating these two forces
So the output energy of the particles is
Therefore, the limit to the cyclotron's output energy for a given type of particle is the strength of the magnetic field , which is limited to about 2 T for ferromagnetic electromagnets, and the radius of the dees , which is determined by the diameter of the magnet's pole pieces. So very large magnets were constructed for cyclotrons, culminating in Lawrence's 1946 synchrocyclotron, which had pole pieces 4.67 m (184 in) (15.3 feet) in diameter.